Typically, semiconductor processing equipment has a number of chambers in which semiconductor processing occurs. Arm assemblies or other robotic devices are generally used to move semiconductor wafers from a wafer handling station to various chambers for processing. When the processing is finished, the wafer is returned to the wafer handling station.
Semiconductor processing is typically done in a vacuum. The wafer handling station includes a chamber and a wafer cassette assembly positionable in the chamber. The wafer cassette assembly includes spaced apart cassette members stacked one on top of another, where each cassette member holds a respective wafer.
For example, the wafer handling station disclosed in U.S. Pat. No. 6,454,508 is a dual cassette loadlock. A workpiece loading interface includes two separate chambers, where each chamber may be separately pumped down. While a first cassette of wafers, from a first chamber is being accessed, a second cassette of wafers may be loaded in the second chamber and the second chamber pumped down. Each cassette of wafers includes spaced apart cassette members stacked one on top of another, where each cassette member holds a respective wafer. Each chamber has a door associated therewith. After the door is opened, a cassette of wafers is lowered through the opening in a motion much like a drawbridge. The cassette of wafers may then be pivoted within the chamber.
Another wafer handling station is disclosed in U.S. Pat. No. 5,905,302. The wafer handling station includes one or more wafer cassette members defining two or more coplanar wafer seats, a movable stem supporting the cassette members, and an actuating member connected to the stem to move the cassette members.
To minimize or reduce contact between a surface of a wafer and a cassette member, contact pads may be used. The contact pads are spaced apart on a surface of each cassette member. However, the wafers have a tendency to walk out from the cassette members due to vibration during operation of the semiconductor processing equipment. As a result, the edges of the wafers may become damaged, or the surface of the wafers may be scratched, or the wafers may even be broken. Damaged wafers reduce productivity and efficiency of the semiconductor processing equipment.